Automated circuit fabrication and direct characterization of carbon nanotube vibrations.

Since their discovery, carbon nanotubes have fascinated many researchers due to their unprecedented properties. However, a major drawback in utilizing carbon nanotubes for practical applications is the difficulty in positioning or growing them at specific locations. Here we present a simple, rapid, non-invasive and scalable technique that enables optical imaging of carbon nanotubes. The carbon nanotube scaffold serves as a seed for nucleation and growth of small size, optically visible nanocrystals. After imaging the molecules can be removed completely, leaving the surface intact, and thus the carbon nanotube electrical and mechanical properties are preserved. The successful and robust optical imaging allowed us to develop a dedicated image processing algorithm through which we are able to demonstrate a fully automated circuit design resulting in field effect transistors and inverters. Moreover, we demonstrate that this imaging method allows not only to locate carbon nanotubes but also, as in the case of suspended ones, to study their dynamic mechanical motion.

Sources of subjective variability in the assessment of left ventricular regional wall motion from contrast ventriculograms.

Intraobserver and interobserver variability in the subjective interpretation of angiographic regional wall motion was quantitated in 135 contrast left ventriculograms showing a wide range of normal and abnormal cardiac function, and the effects of rating-scale complexity and myocardial regional differences were examined. Three experienced observers separately graded endocardial motion on a 6-point scale (0 = normal to 5 = dyskinesia) in each of 5 regions. Scores were also tabulated on a 3-point scale and as normal or abnormal. Average intraobserver agreement (2 evaluations per observer) was 68% using the 6-point scale, 86% using the 3-point scale and 90% for normal/abnormal. Interobserver agreement (3 observers) was 47% for exact agreement using the 6-point scale, 75% using the 3-point scale and 80% for normal/abnormal. Interobserver agreement was 84% within a range of 1 wall motion grade on the 6-point scale. Subjectively normal wall motion was most frequent in the 2 basal segments and least frequent in the apical and anterolateral segments. Disagreements were most frequent in the latter 2 segments, but when normal segments were excluded, these interregional differences disappeared. Thus, intraobserver and interobserver agreement is higher than previously reported, and may exceed 80%. Variability depends on whether regional wall motion is normal, but is also affected by the complexity of the rating scale. The distinctions implied by a 6-point subjective rating scale are probably not reliable, but variability is greatly reduced by use of a simplified scoring system.

Left ventricular mechanics in dilated cardiomyopathy.

The influence of altered chamber shape on the evaluation of left ventricular (LV) mechanics in idiopathic dilated cardiomyopathy (IDC) is unknown. Nine patients with IDC and 7 subjects with normal LV function were studied with simultaneous LV pressure and M-mode echographic recordings in order to derive LV meridional wall stress. The major axis of the left ventricle, determined from the left ventriculogram at rest, allowed for derivation of circumferential wall stress. The IDC group was characterized by larger end-diastolic and end-systolic LV volumes, increased LV mass, depressed angiographic ejection fraction and more spherical LV chamber shape. Both end-systolic meridional (114 +/- 30 kdyne/cm2) and circumferential (251 +/- 73 kdyne/cm2) wall stresses were elevated in patients with IDC, although the ratio of these stresses was less than normal (2.2 +/- 0.1 vs 2.7 +/- 0.2, respectively). LV load alteration with phenylephrine or nitroglycerin allowed for construction of end-systolic stress-minor-axis dimension and end-systolic stress-minor-axis shortening relations. Similar mean slopes of the meridional end-systolic stress-dimension relation were noted in IDC and normal subjects, although the line was displaced to the right in IDC. The slope of the circumferential end-systolic stress-dimension relation was, however, decreased in patients with IDC. Moreover, the end-systolic stress-fractional minor-axis shortening relation in patients with IDC was displaced downward from the normal relation supporting depressed contractile function in these IDC patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of subjective and computer-assisted assessments of angiographic left ventricular regional wall motion.

To evaluate the accuracy of angiographic methods for analysis of left ventricular regional wall motion, we measured the ability of a carefully performed subjective analysis (three independent observers) and that of three computer-assisted methods (centerline, radial, and area) to detect the presence of significant coronary artery disease. Normal ranges were established in 90 studies showing normal wall motion, and accuracy was tested in a second, consecutive series of 43 ventriculograms. The results show that the subjective method best separated those regions with from those without significant coronary disease. The subjective method also demonstrated sensitivity comparable to the centerline and radial methods. Among the computer-assisted methods, the area method was least sensitive but most specific for both anterior and inferior region coronary disease. The centerline and radial methods were highly sensitive, but less specific. When coronary disease was defined by electrocardiographic Q-waves, the area method had superior accuracy. Further analysis showed the following: 1) For the centerline and radial methods, long-axis reregistration of the end-systolic frame resulted in loss of sensitivity but increased specificity for anterior wall coronary disease, and little change in analysis of the inferior wall; 2) inclusion or exclusion of the apex had little effect on predictive accuracy for anterior wall coronary disease; 3) as expected, sensitivity and specificity results of all methods were dependent on the selection of a normal range cutoff value; but when performance was optimized, the subjective and area methods had a higher overall predictive accuracy than the centerline method; 4) It is likely that all three computer-assisted methods could be calibrated to give indications of degrees of hypokinesis, as their results correlated well with subjective observers' evaluations over the entire range of scores. These results should assist in selection of the optimal method for regional wall motion analysis in clinical and research applications. As currently applied, the area method is the most specific of the computer-assisted methods tested; the centerline and radial methods have highest sensitivity and therefore are most suited to detection of mild degrees of hypokinesis.

Effect of heavy cigarette smoking on renal and myocardial arterioles.

While cigarette smoking is felt to damage small vessels in organs not in direct contact with smoke, the kidney has not been considered a target organ. Sections of kidney and myocardium in 40 autopsied subjects without known disease which damage small vessels (21 smokers, 4 ex-smokers and 15 nonsmokers) were examined to determine if the percentage of intima (IP) was increased in small (less than 150 microns) and larger (150-550 microns) arterioles. In both organs and in all vessels, mean IP was significantly greater in smokers. The degree of increase did not correlate with smoking dosage (in pack-years) but did show a positive correlation with age in the kidney but not the heart. In the kidney, at all ages studied, IP was significantly increased in smokers compared to nonsmokers. We conclude that the kidney is another target organ of smoking. Whether this causes clinical disease is unknown.

Effects of nitroglycerin in patients with angina, normal coronary arteries, and left ventricular hypertrophy.

The coronary hemodynamic and left ventricular mechanical responses to nitroglycerin were studied in eight patients with angina, normal coronary arteries, and pressure overload left ventricular hypertrophy (POLVH) and in five control subjects. Elevated mean and end-diastolic pressure and end-diastolic meridional stress characterized the POLVH group, although systolic meridional stresses were not significantly different from the control group. Thermodilution coronary sinus flow and estimated myocardial oxygen consumption declined significantly following nitroglycerin in both patient groups. Systolic and diastolic mechanical loads also decreased in both groups, although diastolic tone remained elevated in the patients with POLVH. The decrease in coronary sinus flow in the POLVH group was in excess of that expected from the decrease in systolic mechanical load, which suggests a combination of perfusion pressure-dependent decreases in coronary flow as well as an increased resistance to coronary inflow in these patients. The beneficial clinical response to nitroglycerin may reflect the lowered myocardial metabolic demand as well as the decrease in diastolic myocardial tensile and compressive forces.